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PETROGRAPHIC STUDIES OF SELECTED BARIUM SULPHATE DEPOSITS IN BENUE TROUGH OF NIGERIA

CHAPTER ONE

INTRODUCTION

1.1       Background of the Study

Barytes is an orthorhombic mineral with chemical composition BaSO4. It possesses one perfect cleavage and two good cleavages, as do the isostructural minerals. The mineral has a specific gravity of approximately 4.5, and it is relatively soft, approximately 3 on Mohs scale. The colour ranges from white to yellowish, grey, pale blue or brown and a thin section is colourless. Barytes (BaSO4) are heavy spar, inert and stable. These properties make them valuable. Barytes, formerly used chiefly as filer and adulterant, is now used in glass and paints industries and the oil well drilling industries which consume 80 percent the world production. Barytes group minerals include the sulphates (SO42_) of barium (barites or barite), strontium (Celestine) and lead (anglesite). The structure of barite has sulphate group lying on a reflection plane, two oxygen of the sulphate group lie within this plane, and two oxygen and minor images across it. Each barium atom is coordinated by twelve oxygen atoms and seven separate sulphate groups. Baryte, the most common barium mineral, is abundant in moderate to low-temperature sulphide veins, being associated with fluorite. It occurs mainly as gauge minerals in metalliferous hydrothermal veins and as veins or cavity filling concretion in limestones, sandstone, shale and clay (Dunham 1984).

Origin Of Barytes

The origin of barite according to Hatch wells (1971) can be supported by the following model:

I.          Anatexis

II.        Differentiation of basaltic magma from the upper and lower crustal rock by fusion.

III.      Carbonitic origin.

Anatexis ; this is the partial melting and recrystallization of pre existing rocks which is attained as high temperature, low pressure and shallow depth (Hatch wells, 1971). The melt composition depends on phase relationships in the solid and the temperature and pressure conditions of melting. (Hatch wells, 1971). Differentiation of basaltic magma derived from the upper mantle and lower crustal rock by fusion olivine crystallizes out of the melt due to reduction in temperature.

STAGE 1; this is the early stage during which Mg/ Fe rich mineral like Olivine crystallize out of the melt, due to reduction in temperature.

STAGE 2; this is the intermediate stage when the rock forming minerals crystallize out of the melt.

STAGE 3; this is the late stage of crystallization during which the residual magma rich in water and volatiles crystallize out. The product of this stage is usually pegmatite rocks in which barite minerals are associated with. Also in this series minerals higher above, crystallize out of the melt before the ones below and the earlier formed minerals may react with magma to form mineral lower in reaction series. Iv carbonitic origin; this is divided into 3 main types;

a)              Late barite replacement carbonites which are commonly ankeritic, sideritic or maganiferous and also contain fluorite and have contained fluorite and may have RE-Th species.

b)             Veins and replacement bodies outside the complex, usually in unaltered wall rock, barites alone, barite plus fluorite or quartz or carbonates.

c)              Residual barites accumulation and supergene barites developed by weathering of carbonitic complexes.

Chemistry Of Barytes

Specimen of barites are generally nearly pure BaSO4. Barium (Ba) can be replaced by strontium (Sr) in a continuous solid solution series from barites to Celestine. Members of this series with a preponderance of Ba, molecule are called strontibarytes and these near the Sr end are called barytocelestine (Heinrich and Vian, 1996). Appreciable replacement of Ba by Pb or by Ca is uncommon and it has been shown that at room temperature only about 6% CaSO4 can enter into solid solution in barites structure. The solubility of barite in water is very slight but it is increased by heating and by the presence of chlorides. When gently heated some crystal of barite deprecipate giving of H2S (Dunham, 1984).

The lead-zinc-barium deposits of the Benue Trough have been known since colonial times. Initial exploration efforts mainly by geologists from the Geological Survey of Nigeria (GSN) between the late 1930’s and the early 80’s led to the discovery of some small to medium-sized deposits in a fairly extensive belt stretching from the southeastern part of the Trough to the northeastern parts.

Tattam 1930 made the earliest report on lead-zincbarite mineralization in the Lower Benue Trough, highlighting the mode of occurrence and mineralogy of the lead-zinc deposits in the Abakaliki area. This was followed by extensive surveys to determine the extent of mineralization in the Abakaliki and Ishiagu areas, (McConnel, 1949; McKay, 1950; Farrington, 1952; Orajaka, 1965). Nwachukwu (1974) determined the temperature of formation of the Abakaliki deposits from fluid inclusion studies and suggested a magmatic origin for the deposits. 

The origin based on circulating connate waters proposed by Olade (1976) was supported by fluid inclusion studies and trace element geochemistry (Olade and Morton, 1985). Ezepue (1984) described the geologic setting of the lead-zinc deposits around Ishiagu, with emphasis on how tectonic fissures influenced the loci of mineralization. Lead isotope (Maurin and Lancelot, 1987) and geophysical studies (Etim et al., 1988) suggested that the most credible lead source for the Abakaliki mineralization corresponds to detrital feldspars which were eroded from the basement and re-concentrated within the sandstone-shale series. The latter supported this claim from 48 electric soundings with correlation from 2 well logs within the vicinity. 

The results of this survey revealed the presence of a sandstone formation probably more than 300m thick at the core of the NE-SW anticlinal structure and the absence of an evaporitic sequence or salt dome up to the depth of 275m. Akande et al. (1988, 1989) used a combination of field evidence, ore microscopy, electron microprobe, fluid inclusion and stable isotope studies on the lead-zinc deposits of the Middle and Lower Benue Trough, and suggested a basinal-brine expulsion model for the Benue ore fluids. The distribution of the lead-zinc-barium deposits in the Benue Trough of Nigeria are restricted to the Albian – Turonian sediments but more widely distributed spatially. They occur along the entire stretch of the basin, but as secluded and widely separated bodies. 

Sediment-hosted lead-zinc-barium deposits can be of the Sedimentary Exhalative (Sedex), also known as clastic-rock dominated sedimentary sequences (Leach et al., 2010) or of the carbonatedominated sequences also known as the Mississippi Valley Type (MVT). The most important characteristics of these two main deposit types are found in Gustafson and Williams (1981), Large (1983), Sangster (1990), Lydon (1996), Sangster and Hillary (1998) and Leach et al. (2005). The general characteristics of the Benue Trough lead-zinc-barium deposits, therefore, are: (1) the ores are epigenetic. (2) They are hosted in carbonaceous shales and siltstones of Albian – Turonian age. (3) They are closely associated (spatially) with igneous intrusions. (4) Ores occur as veins which may extend up to 2km in length. (5) Veins are structurally controlled, and trend NW-SE and N-S.

(6)  The temperature of ore formation from fluid inclusion studies is between 90o C and 200o C.

(7)  They are closely associated with saline springs. (8) The principal mode of occurrence is open space filling (rather than replacement). (9) Wall rock alteration is minimal or non-existent, suggesting that temperature of mineralizing fluid was low and (10). 

The ores are localized in a variety of widely separated rocks, which implies that ore formation is related to regional rather than local processes. In the present work, four mineralized areas were identified and studied in greater detail. These include: (1) the Ishiagu area; (2) the Abakaliki area; (3) the Wanikande-Wanakom area; (4) the Gabu – Oshina area. This paper presents the results of lithologic and structural studies carried out around quarry sites and mining pits in these four mineralized areas.  However, the study tends to examine the petrographic study of a selected barium sulphate deposits in Benue trough of Nigeria.

1.2       Statement of the Problem

High priority has been placed on exploration and exploitation of the barite deposits in the country since the  Federal Government proposed the banned importation on barite many years ago. The bulk of the barite mined in different parts of Nigeria are used as weighting agent in oil and gas drilling operation. Furthermore, the country has put more attention on the oil and gas industry which produces the highest GDP yearly and demand for barite may probably continue to grow giving the fact that further exploration and development of wells will consequently boost barite consumption.

So far, as can be ascertained, there has not been any detailed work on the assessment and optimization of barite deposit in the South-East region of Benue state. There is therefore, a need to characterize the barite mineralization in the area using major oxides and trace elements composition and other physical parameters which will serve as guide to further exploratory work. Hence, this study was conducted to investigate petrographic studies of selected barium sulphate deposits in Benue trough of Nigeria.

1.3       Objectives of the Study

The main objective of this study is to investigate petrographic studies of selected barium sulphate deposits in Benue trough of Nigeria. Specific objectives include;

i.   Identification of barite occurrence in south-east of Benue state.

ii.     Partial beneficiation of the barite ore.

iii.   Characterization of the barite ore from the study area.

iv. Determination of the physical properties.

v.        comparison of the barite ore with the API and OCMA standards as used in oil and gas industry.

1.4 Research Questions

i.   How does barite occur in south-east of Benue trough of Nigeria?

ii.         What are the partial beneficiations of the barite ore?

iii. What is the characterization of the barite ore from the study area?

iv.        What is the determination of the physical properties?

v. What is the relationship between barite ore with the API and OCMA standards as used in oil and gas industry?

1.6       Significance of the Study

This study will look intensively on the petrographic studies of selected Barium sulphate deposits in Benue Trought of Nigeria. This study will be of immense benefit to other researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. 

This study contributes to knowledge and could serve as a guide for other study. The recommendations will enhance academic performance.

1.7       Scope of the Study

This study examines the use of barite ore bedded in the region of south-east Benue state as substitute for weighting material which are imported from oversea and used in the Nigerian oil and gas industry. The study includes:

1.  the processing of the ore (barite) with different compositions through gravity separation

2.  the material characterization of the barite ore with:

i.  Energy Dispersion X-ray Spectroscopy (EDS);

ii.  Scanning electron microscopy (SEM);

3.  the determination of the effect barite characteristics on mud density

4.  the determination of the rheological properties

i.        apparent viscosity

ii. plastic viscosity

iii. gel strength

iv. yield point

1.8       Limitations of the study

The researcher is a student and therefore has limited time as well as resources in covering extensive literature available in conducting this research. Information provided by the researcher may not hold true for all institutions but is restricted to the selected organization used as a study in this research especially in the locality where this study is being conducted. 

Financial constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet, questionnaire and interview).

Time constraint: The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work.

Finally, the researcher is restricted only to the evidence provided by the participants in the research and therefore cannot determine the reliability and accuracy of the information provided.

1.9       Definition of Terms

Petrography:  Petrography is the study of rocks in thin section by means of a petrographic microscope (i.e., an instrument that employs polarized light that vibrates in a single plane). Petrography is primarily concerned with the systematic classification and precise description of rocks.

Study:  the act of making an effort to learn by reading, practicing, or memorizing. 2 : a careful investigation or examination of something the study of a disease. 3 : a room especially for study, reading, or writing.

Barium Sulphate:  Barium sulfate (or sulphate) is the inorganic compound with the chemical formula BaSO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium and materials prepared from it.

Oil:  a slippery or viscous liquid or liquefiable substance not miscible with water. oil, oil color, oil colournoun. oil paint containing pigment that is used by an artist. petroleum, crude oil, crude, rock oil, fossil oil, oilnoun

Ore:  a naturally occurring mineral containing a valuable constituent (such as metal) for which it is mined and worked.